Noritz Tankless Water Heater Making Loud Noise [Reasons + Solutions]

The leading reasons behind your Noritz tankless water heater making loud noise are:

  • A dirty flow sensor.
  • Loose parts. 
  • Sediment build-up and restricted water flow.
  • Leakage
  • And, water pressure fluctuations.

While you’re struggling to fix your heater noise issue, first check out the flow sensor to ensure that it is in perfect working condition. Plus, tighten the loose parts and fittings of the heater with a wrench. If the sound source is the heat exchanger, you need to clean up the carbon buildup from there. 

noritz tankless water heater making loud noise

Hopefully, you will get the solution. If it isn’t proving well, go on reading…

Table of Contents

Noritz Tankless Water Heater Making Loud Noise [Reasons + Solutions]

Here are the details of all the common reasons related to your Noritz tankless water heater creating loud noises and a guide on how to eliminate the problems. Let’s read between the lines.

Note: You can also read how to fix the Noritz tankless water heater no display.

1. Dirty Flow Sensor

A dirty flow sensor is one of the major culprits for your tankless water heater generating loud noise.

Typically, Noritz water heater heat flows based on the spinning of the wheel of the flow sensor. Plus, the flow sensor detects the incoming and outgoing water temperature and initiates the heating process. 

noritz tankless water heater flow sensor 

But when the sensor is bad, a vacuum siphons away from the unit and can’t read the flow momentarily. As a result, it produces a loud sound during the operation.

Again, if the gas controller loop can’t give feedback via the flame temperature sensor, you may hear a loud noise from this unit. Whatever the reasons, solve the problems by following tips.


The first thing is to identify the source of the noise. For instance, locate the sensor and monitor whether it is clogged by dirt and debris. But before that, turn off the power and gas supply. Remove the outer 4 screws and disconnect the front access panel. 

Let’s follow the below tips to locate and access the flow sensor on your Nortiz tankless unit:

locate and access the flow sensor on your Nortiz tankless unit

Next, pull out the flow sensor and remove the sensor impeller from the housing. Disassemble the sensor and inspect whether the parts are blocked by dirt. 

If so, carefully clean the dirt from each of the little parts using a soft cloth. But make sure you are not damaging any parts while cleaning. 

After cleaning, reassemble the flow sensor, and insert the impeller into the cylinder. When done, put the flow sensor back into the heater. Finally, replace the front cover in place and turn on the gas. 

Reconnect the electrical power to run the heater again. Slowly pressurize your heater. Hopefully, your flow sensor won’t be troublesome further.

2. Accumulation Of Sediment

Building up sediment is the next culprit for causing a loud noise in your water heater. A tankless water heater builds up minerals, especially if you are living in hard water areas.

Unfortunately, you will hear the below sounds if the sediment accumulates in your system. For instance:

  • Rambling– Normally builds up sediment in the system.
  • Popping– When the huge sediment starts to break from the heat.
  • Sizzling, Hissing & Crackling—sediment in the base of the tank.

Besides, this sediment may break the pipes and even can damage your beloved heater. If that happens, your heater will make a sound like a water hammer. However, you can operate a flush on your system by yourself to stop it from noising.


To remove sediment and reduce the noise from your heater, flush out your system with vinegar at least once a year to protect against further problems. To do so, you will need the following things.

things are needed to remove the sediment
  • Grade White Vinegar (3-4) Gallons
  • 5- Gallon size Bucket
  • Submersible pump
  • 3-4″ Hose Drain Connections and Screwdriver. 

Once you have all the above accessories, go through our comprehensive guide or watch the below video to descale your Noritz tankless water heater effectively.

remove sediment

Additional Tips: Yet, if the flushing system can’t solve the problem, add an arrester to the water system line to get rid of water hammering. Plus, you need to set up an automatic or manual air vent at the highest point of the waterline to avoid further problems. 

In case, you are living in a hard water area, it’s better to install a water softener or sediment filter to prevent scale buildup on the heater elements, water lines, and faucet parts. 

3. Loose Parts

If there is no issue with the flow sensor or heat exchanger, we bet the noise comes from the loose parts of your heater. This issue may occur if the pipe connections, heating elements, or any other parts become detached in-course of time.

noritz tankless water heater loose parts

Basically, your Noritz heater will make a noise like vibrating, humming, buzzing, and hammering  if:

  • The direction of the water flow changes suddenly.
  • It gets insufficient space for condensation.
  • Water is flowing under the heating element.

After all, the above issues loosen the heating elements and water supply lines. Whatever the case, here is the solution for you.


To resolve the issue, first, find out the source of the noise. After identifying any loose parts, take a proper wrench and socket and tighten them to prevent them from entering the flow of water. 

Plus, we would suggest you recheck whether the water lines are secured in their right place, such as—copper for copper and metal for the metal pipe. 

In addition, consider installing a spacer pipe or hammer arrestor close to the valve to avoid intolerable noise. If the issue isn’t fixed yet, there might be trouble with water flow. 

4. Restricted Water Flow

Restricted water flow is another common reason for creating a loud noise in your tankless water heater. When your tankless water heater sounds quietly irritating, screeching, or screaming, it is a sign that the water flow unit has been blocked in any way.

This is most likely related to the water shut-off valve of your tankless water heater. Either it is partially opened or closed at all. Apart from this, if the water filter screen clogs by sediment deposits, it will also prevent water to flow freely to the unit. 


To ensure a restriction-free water flow, first, inspect the water shut-off valve to see whether it is opened all the way. The valve lever should be in line with the water pipes. When done, remove the front access panel of your heater to access the water filter screen. Clean it with a brush or under running water. 

After doing all the above steps, you can expect to run water through the unit without any distractions. 

If still, you’re encountering the same issue, then the pressure release valve may be a cause for creating noise.  

5. Pressure Valve Issues

An unpleasant ticking noise is coming from your tankless due to an incorrect setting of pressure relief valves, installed near the hot water outlet. The pressure relief valve is supposed to lower the heater pressure back down to safe levels by relieving excess pressure. 

pressure valve issues

But once you’ve set the valve too high, it will start creating a high-pitched noise. At times, the defective valve is the culprit itself. 

If the source of the sound is this pressure relief valve, we’ll recommend turning off the gas & electric supply immediately and fix the issue. 


First, inspect the relief valve to see if it is fully opened. If not, rotate the valves until they are in the right position.  If the pressure relief valve is leaking or being damaged,  it will need to be replaced

Along with replacing the pressure relief valve, you need to adjust the pressure of your water heater. You need to keep the valve pressure limit within 50 psi by releasing extra pressure. 

 For instance:

  • First, remove the cover and locate the 4 buttons on the right side of the unit. You will find there are UP and DOWN buttons with Manifold Minimum and Manifold Maximum buttons. 
  • Set the minimum and maximum settings using the manifold button on the unit. We’ll recommend you start with the minimum setting first.
  • Turn the water valve ON to simulate the MIN pressure flow. Press the Up and Down buttons repeatedly until you set the pressure. Again, do the same thing with Maximum Button. 
  • After that, ensure the water valve is in a good position and the vent system is running properly. 
  • Though the Noritz inlet pressure is 150 Psi, it doesn’t mean that you would operate with such high pressure. So, manually, the set point should be 50 Psi. Expectantly, the issue will be fixed.

But when your pressure valve is in good condition, the noise might come from leakage in the heater. 

6. Issued With Leakage

Your water heater is running, but you are hearing a hissing sound. This is normal. But if the sound goes beyond the limit and there is no hot water, be sure the Noritz water heater leakage is a major culprit behind it. 

noritz tankless water heater leakage

In fact, moisture, such as water on the floor or shipping out under walls means that there is a leak in the water line. The issue is really a matter of concern that should be fixed ASAP.


To resolve the leaks, first turn off the cold water supply and shut off the electrical breaker. Now, check for leakage and identify the leakage source. 

Check out the connections of the heater.  Make sure that all of the pipes and fittings are secured enough. Fix or replace the defective parts. If you find it difficult to find the leakage source, call a professional to complete this task for you. 

7. Problems With Fans

Sometimes your heater may make an intolerable noise because of the clogged fan as it restricts the fresh air supply.

Typically, a water heater’s fan induces combustion air and even helps significantly increase the output of hot water when many fixtures are being used at a time. But if it is in the out-of-balance wobble, the blades of the fan scream.

Besides, the fan is knocking or scraping due to-

  • Dirty and debris logged on fan blades or the gas unit.
  • Insects or lizards stuck with the fan’s blade.
  • And set too high a water temperature level.


First off inspect the fan and make sure it is fit well in its position. Also, check for obstruction in the fan blades. If so, clean around it as needed by using a brush and also brush under the burner plate to clean dirt and debris. 

Then, apply compressed air to remove the particles. Finally, ensure that your water heater isn’t making loud noises. If you can’t bring your heater back to its usual condition, call a professional to inspect what is wrong with the water heater.

Maintenance Of The Notitz Tankless Water Heater

Noritz is an energy-efficient and excellent investment to get an endless supply of on-demand hot water in your home. But you may have experienced some noise issues with your heater.

maintenance of the notitz tankless water heater

However, periodic maintenance ensures that it will ultimately reduce loud noise and keep your heater fit.

Plus, periodically look into heating elements. If the system gets overheated, shut down the unit immediately and call a professional to inspect minutely and maintain it to bring back your heater in working condition. Because a tankless water heater lasts long if you maintain it correctly.


Why does my water heater still knock after flushing or draining?

Your water heater is knocking due to accumulated hard sediment even after flushing. Because the hardened chunk of pebble is too difficult to drain out. So, install an arrestor to get rid of this issue.

Is it normal to make a noise with a tankless water heater?

A tankless water heater will make a slight noise while heating water. But when the noise level crosses 90 decibels, that causes concern,

What is the best temperature setting to reduce loud noises?

The water temperature is typically set at 115- 125°F, but it can be reduced to 110°F. This setting will reduce noise by causing too high pressure and extend the life of your tank.

Final Words

Now, you have a better understanding of why your Noritz tankless water heater is making loud noises and what different sounds mean. 

Whatever the cause, follow our exclusive guide to resolve your water heater sound problems. Plus, keep your water heater under periodic maintenance as it will help your heater to work quietly and efficiently for years.

Still, if you struggle to fix your trouble, don’t be hopeless. Rather, leave a comment for us. We will come back to you ASAP.

About William

William is the founder of He has real life practical skills in fixing smoker & heating appliance issues. He loves to share his knowledge & helps others in fixing their appliances & saving their money. William firmly believes that anyone can repair his or her unit with the correct guidance & knowledge. See more at about us.

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